1. Field of the Invention
The present invention generally relates to a drive force transmission apparatus. More specifically, the present invention relates to a manual transmission capable of an automatic transmission control, noises called gear slapping sounds caused by collisions of gears defining a gear set in a set shift range at an engagement part thereof are reduced.
2. Background Information
Some conventional transmissions are provided with two drive transmission paths using a pair of discrete clutches that selectively input an engine rotation into the drive transmission paths. One example of this type of conventional transmission is described in Japanese Unexamined Patent Publication No. 8-320054. This transmission is a manual transmission, but at the same time, can control the automatic transmission control. More specifically, such transmissions are provided with a pair of input shafts with one in each of the respective transmission paths that are selectively engaged by the operation of the clutches during a gearshift operation. Thus, a gearshift operation can be perform by a switching gear shift in which one of the clutches connected to one the input shafts is engaged and the other is disengaged. During this gearshift operation, the clutches are operated so that torque is being constantly transmitted from the engine to the differential gear system. Thus, one feature of the gearshift control for this type of twin clutch transmission is that a so-called torque cutting phenomenon does not occur. The so-called torque cutting phenomenon is where torque transmission from an engine becomes “0” during the gearshift operation.
The so-called torque cutting phenomenon occurs in typical clutch transmissions that are provided with one clutch and one input shaft. In other words, in the gearshift operation for the typical clutch transmission provided with a single clutch and a single input shaft having a plurality of gear sets attached between the input shaft and a countershaft, during a first time period, the clutch is disengaged such that the torque transmission from the engine is completely cut off. Then, the current gear shift range or ratio is disconnected during the first time period, and another gear set is selected for a target gear shift range or ratio. Finally, the clutch is re-engaged during a second time period to complete the gear shift operation. Therefore, the torque transmission from the engine becomes “0” during the period of time during the second time period.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved drive force transmission apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.